This invention pertains generally to air makeup and recirculation systems and more particularly to such operations where purification of the air is required.
Air recirculation and makeup for nuclear reactor plants require purification flow in alternate paths to maintain the purity of a fluid within the plant in the event the plant becomes contaminated. For example, in the environmental control for a nuclear reactor power station control room purification flow paths are used in the unlikely event of an accident to protect plant personnel. Generally, there is provided a positive supply of conditioned air to maintain positive pressure within the control room relative to the surrounding environment. A sustained positive pressure within the control room reduces the unfiltered in leakage of air that is assumed would occur if the control room was not pressurized. Normal leakage paths consist of cracks and seams in walls, floors, ceilings and fluid systems.
The environment in the reactor control room is normally controlled by recirculation which draws air from the control room and recirculates it through an air conditioning unit designed to maintain a selected humidity and temperature. In addition, makeup air communicates with the air conditioning unit to makeup for normal exfiltration and sustain the desired pressure. In the unlikely event of an accident involving the release of contamination it is desirable to filter the incoming air passing through the makeup system to avoid the introduction of contamination into the control room environment. Under such circumstances it is also desirable to purify the air recirculated to the control room to reduce the effects of any contamination that might be otherwise introduced. If systems to effect the purification were placed in series with the normal makeup and recirculation flow, it would greatly increase the required filtration capacity above practical limits and effect their reliability. Alternatively, if a makeup filtration flow placed in parallel with the normal makeup flow path it would require expensive and elaborate means for closing the normal flow path under emergency conditions to assure that no filter bypass leakage existed, so that the efficiency of the filtration would be increased. Additionally the control of make up air flow would have to be modulated to control the building pressure and thereby would not allow full flow air filtration at the optimum capacity of the filtration operation. Recirculation through alternate parallel filters in a bypass mode would allow filter bypass air flow with resulting lower filtration efficiency. Accordingly, a new method of maintaining pure the air in the work area of a nuclear-reactor plant is desired. It is desired that the makeup and circulation of the air shall have an alternate purification capability that minimizes the capacity of the purification required while maximizing efficiency.